I hear he can swap out a transmission in an instant
I don't think I trust Goku with my car. I know I don't trust child Goku. Kid thought cars were demons, at first, and managed to blow a hole into one his first time trying the Kamehameha.
Adult Goku just doesn't seem mechanically adept. Like, not even going down the "Goku is stupid" train(He can be decently intelligent, when the need arises), but I just can't picture him going "I wanna know how a car works".